The present invention relates to a method for producing dimensionally correct compacts of powdered material on a press in a mold having at least one top plug and at least one bottom plug between which plugs said powdered material is compressed. The present invention also relates to an apparatus for carrying out the foregoing method.
From Federal Republic of Germany 2,951,716 C2, a method is known for pressing moldings having at least one step of metal powder, by which moldings of constant height and density can be produced. For this purpose, the variation of the pressing force of the force plugs is measured as a function of the distance traveled, and is stored and compared with predetermined distance-dependent desired values. The precision in height of the compacts is in this connection assured by mechanical stops and by the stroke of the top force plug which can be set to a fixed value. The constant density is made possible within given limits of precision in the manner that the filling volume of the mold is reduced in the next operating cycle when the mentioned comparison of the pressing force has shown that the desired value has been exceeded. The reverse process is employed if the desired value has not been reached.
In this way, reaction changes in the properties of the metal powder used or other changes (for instance occurrence of given mechanical oscillations) which, in the final analysis, affect the bulk density of the powder and thus the compression properties of the powder introduced into the mold, can be reacted to. To be sure, in this case, the correction can act only in connection with the next compact since no change in the filling volume of the mold is possible any longer in the case of the compact on which the differences from the desired value were noted. The known method, however, results in definite improvements over the prior art which was known up to that time with respect to the simultaneous maintaining of density and precision of shape of the compacts. In the event of particularly high demands on the precision of the compacts, however, this method is not always sufficient and it may lead to considerable rejects due to the unavoidable dead time of the method of regulation used.